We present a model and process independent study of the contributions
from non-Standard Model physics to the oblique parameters S, T and U.
We show that within an effective lagrangian parameterization the expre
ssions for the oblique parameters in terms of observables are consiste
nt, while those in terms of the vector-boson vacuum polarization tenso
rs are ambiguous. We obtain the constraints on the scale of new physic
s derived from current data on S, T and U and note that deviations in
U from its Standard Model value would favor a scenario where the under
lying physics does not decouple. (C) 1998 Published by Elsevier Scienc
e B.V. All rights reserved.